The behavioral excitation response to amphetamine has been found to be blocked by haloperidol but not by propranolol or thymoxamine; this suggests specific dopaminergic mediation of this response in normal man. The norepinephrine and pressor responses, on the other hand, are blocked by propranolol, suggesting mediation through beta-adrenergic receptors. None of the blocking agents studied significantly blocked the hormonal responses to amphetamine. Haloperidol caused a significant potentiation of the prolactin response. A pilot study of the effects of intravenous gamma amino butyric acid was performed in 6 patients and 5 normal controls. A number of subjects experienced dysphoric effects. No significant effects on hormone levels were seen. Eleven bipolar patients and 14 controls participated in a study of sensitivity of melatonin secretion to suppression by light. Euthymic patients were found to be more sensitive than controls; this may be a trait marker for vulnerability to depression.